This invention relates to the field of rotating fluid film (hydrodynamic) bearings and provides a solution to problems inherent in prior art bearings that use compound curved bearing surfaces supporting radial, thrust and moment loads. The present invention utilizes the principle of operation of the SWING-PAD BEARING described in U.S. Pat. No. 3,930,691 issued Jan. 6, 1976, in a bearing assembly using compound curved bearing surfaces to carry radial, thrust and moment loads.
In essence, that patent discloses a hydrodynamic bearing pad including a movable face portion that is adjacent to a relatively movable load applying or supporting surface in the presence of a lubricant, the face portion of the bearing pad being mounted for swinging motion relative to a base element underlying the surface portion about a swinging axis or center located toward the relatively movable load applying or supporting surface and away from the face portion of the bearing pad to enable generation of the lubricant wedge. Motion of the moveable base portion of the pad relative to the load applying or supporting surface under operational conditions, as described in that patent, causes the pad face portion to swing in minute amounts to an inclined position relative to the load applying or supporting surface under the combined influences of load and friction forces to produce a wedge-shaped gap that converges in the direction of motion of the load applying or supporting surface relative to the face portion of the pad. Multiple such bearing pads are normally provided in a typical bearing installation for supporting a relatively moving load applying or supporting member. Lubricant drawn into the multiple gaps as a result of relative motion between the bearing surfaces and hydrodynamic action maintains the face portions of the pads and the adjacent relatively moving surface out of contact with each other instantaneously upon onset of relative motion, and during the operation of the bearing.
The shape of the lubricant wedge associated with each bearing pad self-adjusts during operation of the bearing under varying load and speed conditions due to its unique design. Specifically, the face portion of each pad is joined to an underlying base element along an arcuate interface having a center of curvature located substantially at the desired center of swinging motion of the face portion. A curved, laminated, elastomer-nonelastomeric material is disposed between the face portion and the underlying base element of each pad, and is bonded on each side to both elements. The laminate material is compliant in the shear direction (parallel to the arcuate interface between the face portion and the underlying base element) but is essentially rigid in a radial sense (perpendicular to the arcuate interface). Therefore, the face portion of each bearing pad can readily and is actually forced to swing to a slightly inclined position about the center or axis of swing under the influence of friction and load forces applied to its surface by the load supporting member while still maintaining its basic position in the bearing assembly.
My earlier patent referenced above discloses radial and thrust bearing embodiments utilizing the swing pad concept. However, the present invention is intended to utilize the same principle in a combined radial and thrust bearing that utilizes compound curved bearing surfaces, the swing pad bearing overcoming problems encountered in the prior art in situations where it is desired to use such a bearing for supporting high radial loads.
More specifically, it is well known that the rotary part of plain journal radial bearings with lubricated continuous sliding surfaces actually runs slightly eccentric with respect to the longitudinal axis of the bearing, and this eccentricity permits the generation of a wedge of lubricant between the relatively moving bearing surfaces. The wedge of lubricant, through pressures generated by hydrodynamic action, in turn keeps the bearing surfaces apart so that surface-to-surface contact is avoided and frictional resistance to motion is minimized.
In situations where a sliding bearing having both radial and thrust capacity is desired, it has been proposed to use compound curved surfaces of various forms (e.g., a ball in a socket). The problem here is that the compound curvature of the continuous bearing surfaces tends to prevent the moving element of the bearing from assuming its eccentric loaded rotating position at which the lubricant wedge is formed when the bearing is loaded in a thrust sense. The thrust bearing surface, being uniformly curved about the rotational axis, tends to hold the rotating element at the center of the bearing and therefore a radial load supporting lubricant wedge can not be developed by the bearing because hydrodynamic pressures are not generated in the lubricant film to the extent necessary to keep the bearing surfaces apart.
A hydrodynamic tilting pad arrangement could be envisioned for such an application, but the required compound curvature of the bearing surface of the tilting pad, along with the variable nature of the radial and thrust loads, results in the position of the center of pressure acting on the tilting pad elements to be unpredictable. Since the center of pressure in a tilting pad bearing arrangement must be virtually in line with the tilt pivot point to prevent instability of the tilting segment of the bearing, clearly a tilting pad bearing had deficiencies which limit its application in a bearing of the type presently under consideration.